docs: def to_op(self):
          """
          Extracts the modification operation from the set.
  
          :rtype: dict, None
          """
          if not self._adds and not self._removes:
              return None
          changes = {}
          if self._adds:
              changes['adds'] = list(self._adds)
          if self._removes:
              changes['removes'] = list(self._removes)
          return changes